How would you play this. Doesn't this make the PC pretty much at an end at this point?

I have not read a way to remove the mark. The only thing I can see is a downward spiral into chaos which would than be the end of a PC. What would be the point, on the GM's side , to give a mark to someone.

Generally, a PC has really got to work hard to earn a Mark. I mean, you don't earn the love of a Chaos God by being a run-of-the-mill adventurer. I'd only give out a Mark of Khorne if, for example, a PC soldier was getting WAY too into his work, and using over-the-top violence to solve every minor difficulty. Likewise, you don't get a Mark of Slaanesh without engaging in outrageous debauchery. It's not something you get from "normal" behavior.

I have a question instead:Do the mark go socketed somewhere, maybe in a talent slot, or it's just a permanent addition?

@Master yoda:I think Marks are designed mostly to NPCs, but if you are interested I think they stick a lot to a rearranged campaign where you're player are training to please a Dark god, maybe even starting out as Marauders in Norsca! Some Players would ove that!

Yea, these things aren't going to see any use in my games. Once a pC gets a mark, they're lost to chaos.

I have installed however, temporary marks for players who make "evil" or debauched choices. Examples include:

killing innocents, allowing innocents to die without lifting a finger, helping chaos, working for the bad guy, stealing some dude's wife, destroying property and leaving people destitute (i.e. burning a farm, but not actually directly killing a family), and the cardinal sin: Burning Down Taverns.

I would not let a PC have such a thing without a very clear story line. Corruption and madness or mutation would have to come first.

I see these as npc stuff really, which is mostly how I see mutation too given its consequences.

I think the marks work fine with PCs, but you have to have a player who is happy to run with it. He has to accept that this is the beginning of the end and be prepared to play his character as a victim. Istm there's loads of RP and fun to be had for the right player in the right group. But using them as some sort of adversarial attack upon the PC is asking for resentment.

While there is no real precedent in the WH world, it might be an opportunity to allow the PC to try and crawl his way out of the pit into which he's just found himself. For example - somewhere in the mountains is a truly blessed priest of Shallya. The priest is old or her health is failing, but she holds the only hope of removing enough corruption for the PC to be just shy of receiving a mark. Of course Nurgle would be involved - both trying to hinder the PCs, but also trying to kill the priest. Add in plenty of opportunity to fall even futher...wih the threat that there is a point of no return and that there will be no hope at all for the PC if they fall too far.

While doing this might be a cheat in some people's eyes, if you and your players are having fun with their PCs, and it won't hurt your overall campaign, I don't see why it couldn't be allowed - once. Removing that much corruption takes a lot out of a dying priest,a fter all. Plus, afterwards, you still have other quests to remove the rest of the corruption......